Lead coating process and material



United States LEAD COATING PROCESS AND MATERIAL Henry A. Wagner,Cleveland, Paul Golar, South Euclid, and James R. Kusa, Maple Heights,Ohio, assignors to The E. F. I-lauserman Company, Cleveland, ()hio, acorporation of Ohio 7 Application December 2, 1955 Serial No. 550,759

4 Claims. (Cl. 117--13il)- No Drawing.

This invention relates as indicated to lead coatings,

more particularly to protective coatings for metal.

surfaces subject to corrosion, especially iron, steel and ferrousalloys.

The tendency of' the less noble metals to revert to their naturallyoccurring states has been recognized since their first employment, andmany dilferent' methods have been adopted in an attempt to prevent,arrest or inhibit such corrosion or rust-ing. It has been. estimatedthat the annual monetary loss due to corrosion in. the United.

States alone is in excess of $5,5 00,000,0O0. Of course, indirect lossesdue to. escape of such materials .as oil, water, natural gas and otherfluids from corroded pipe lines and losses due to down time intransportationfacil-F ties and manufacturing plants are difficult toappraise accurately. It should also be appreciated that construc- Vferrous metals: in use; any method of protecting the same even slightlymore. efiectivelythan methods currently employedwould result in. atcomparable extremely large annual dollar saving.

Each of the knownmet h'ods of protecting ferrous metal surfaces hascertain inherent deficiencies and each such method will ordinarily beemployed only in. certain selected fields of use. Protective organiccoatings; which include the paints and lacquers; are reasonablyeffective as long as the protective film is not broken, but they tend tobe rather expensive and often their cost is justified on the basis oftheir decorative qualities equally with their protective qualities. Theapplicationof metallic coatings both by hot dipping and electroplatingis also an old cart. The'.les.s, noble metals-suchas'zinc are generallyanodic with respect to ironin most environments and are classified assacrificial. The protective coating gradually corrodes away and affordsconsiderable protection as long as a continuous filin remains. There aresituations, however, where: zinc: as: well as. lead, tin, cadmium andaluminum will reverse its potential with re spect to iron andconsequently the position in the electromotive series cannot be whollyrelied upon as an infallible index for predicting the glavanic behaviorof metallic couples in all, environments. Coatings of nonsacrificialmetals such as nickel and coppenmay also form galvanic cellswith. ironalthough-the current flow is in .the opposite directionr to that in. thecase of the sacrificial metals, resulting in accelerated corrosion ofthe basemetal wherever the coating is broken or porous.

lacquers, phosgalvanizing, and other platatent ice Relatively thickcoatings of such non-sacrificial metals are accordingly commonlyemployed.

Hot dip methods of applying protective metal coatings have certainadvantages over similar coatings electrodeposited but also displaycertain inherent weaknesses. Thus, hot dip galvanized steel may developcracks when flexed due to the formation of a hard zinc-iron alloy whichis brittle and has poor adhesive properties. The hot dip method and: theelectroplating method both tend to produce coatings rather non-uniformin thickness.

It is accordingly a principal object of the present invention to providea protective lead coating for metal surfaces subjectto corrosion,particularly iron, steel and the ferrous alloys.

Another object is to provide such coating which. will be considerablyless expensive than other coatings'commonly employed for a like purpose.

A further object is to provide such coating and methodof application ofthe same which will be adapted to sub stantially all sizes and shapes'ofarticles to be protected and will aiford a predictable uniform degree ofprotectron.

till another object is to provide such coating which will not interferewith subsequent working of the article or the application of otherdecorative coatings and the like but instead will facilitate the same.

Yet another object is to provide a method of lead coating by chemical:displacement and a bath suitable for such purpose which will beinexpensive and easy to" maintain with a minimum of supervision andadjustment.

Other objects of the invention will appear as the description proceeds.

To the accomplishment of the foregoing and relatedends, said inventionthen comprises the features hereinafter fully described and particularlypointed out in the claims, the following. description setting forth indetail" certain illustrative: embodiments" of the invention, these beingindicative, however, of but a few of the various ways in which theprinciple of the invention may beemployed.

Generally stated, our invention comprises the provision of a continuouslead coating on the metal surface to be protected by chemicaldisplacement from a water bath containing the lead ion in solution, suchbath having a lead ion concentration of at least about 1 gramer literand awater soluble addition agent containing alkylene oxide condensationproduct, such bath als0-having an acid: pH'.

More particularly, we have discovered that ifi the proper type ofaddition agent (ordinarily a surfactant)- be selectedas indicated above,superior lead-deposits m'ay beobtained by chemical displacement from abath" inwhich: the leadion concentration is relatively low, pre erably'from: about. 5 grams; per liter to about 8'5 grams p'er' liter. The bathshould: desirably be heated to atem' perature of from about 150 F. tojust below the boiling point of the bath for bestlresults.

Examples of water soluble lead salts which may be" utilized in.accordance with our invention, listed in theorder of. preferencehavingregard to the quality of the deposit formed, are as: follows:

Formate I Fluoborate Perchlorate Fluosilicate Acetate Citrate:

' Glycol'ate Tartrate- Lactate Malate Pr'opionate: Nitrate SulphonateChloride muchpreferred.

excellent deposit under the operating conditions of our invention, maynevertheless have explosive properties when improperly handled and itwill accordingly probably not often be used in practice. Similarly, leadacetate, while producing a superior deposit, has a rather unpleasantodor which is likely to militate against its widespread use. The leadcitrate and lead tartrate do not produce as refined deposits as most ofthe other salts listed, and furthermore require to be solubilized byadditions of solubilizing agents such as sodium citrate and sodiumtartrate. Lead chloride is not very soluble, and neither it nor leadnitrate are very satsfactory although deposits can be obtained at verylow lead ion concentrations on the order of 1 gram per liter, forexample.

- When the lead salt is a salt of an aliphatic mono-basic acid(preferred), e. g. lead formate and lead acetate, the water solutionshould contain from about 5 to about 130 grams per liter of the leadion, and preferably from to 40grams per liter. It is a most unexpectedfeature of our invention that our new lead coating process operatesespecially well at such low lead concentrations. A pH of from 2.5 to 5.0or slightly more is suitable but a pH of from 3.4 to 4.2 is preferred.An elevated temperature of from 170 to 210 F. considerably speeds theoperation.

When the lead salt is a salt of an aliphatic mono-basic hydroxy acid, e.g. lead glycolate and lead lactate, the same rules and limitations applyas those given above for the lead salts of aliphatic mono-basic acids.

When the lead salt is a salt of an aliphatic poly-basic hydroxy acid, e.g lead tartrate and lead citrate, the water solution should contain fromabout 1 to 30 grams per liter of lead ion, and preferably from 5 tograms per liter. A pH of from 5 to 6 is best. Ordinarily a solubilizingagent such as the ammonium or alkali metal salts of these same acidswill be employed to bring the desired amount of lead salt into solution.

. Among the inorganic lead salts, lead perchlorate is by far the mosteffective for our purpose. A pH of from 1.2 to 3.0 is suitable, but from1.5 to 2.5 is preferred.

Lead ion concentrations for preferred specific examples of suitable leadsalts are as follows:

In the case of lead formate and lead glycolate, noted above, the upperrange of suitable lead ion concentration is limited merely by themaximum solubility of the salt.

While not preferred, lead gluconate, lead maleate, and lead di-glycolatemay also be employed. W

In most cases the lead salt may be most conveniently prepared byreacting litharge with the proper acid. Thus 28 pounds of litharge (PbO,91% Pb) may be added to 80 gallons of water at a temperature of l80-190F. and agitated while 1.8 gallons of 90% formic acid is next added. Whenthe litharge has entirely dissolved, water is added to bring the totalvolume to 100 gallons.

We have found that extraordinary improvement is obtained in thethickness, density, adhesion and corrosion resistance of the leadcoating produced on ferrous articles by chemical displacement uponimmersion in the solution of such lead salts if a small amount of analkylene oxide condensation product with an organic compound containingan active hydrogen atom is incorporated in the bath. As a practicalmatter, these will ordinarily be ethylene oxide and propylene oxidecondensation products with organic compounds. Their production is wellunderstood by those skilled in the art.

These materials are generally useful as surfactants or wetting agentsand should, of course, be stable at operating temperatures (ordinarilyin excess of 170 F.). Likewise, it is much preferred that they be fullysoluble in the relatively small quantities employed, although thoseforming cloudy or milky solutions perform satisfactorily. If theaddition agent tends to remain at the surface of the bath, it is likelyto be depleted by drag-out as coated articles are removed from the bath.It is apparently not merely the surfactant qualities of the additionagent which render it so effective for our purpose inasmuch as othertypes of surfactants produce little or no improvement. The non-ionicaddition agents appear generally more suitable and effective in lowerconcentrations, but anionic and cationic agents may also be employed.

either saturated or unsaturated, x or x-l-y or x+y+z representing atleast 3, normally 10 to 20, and up to moles of ethylene oxide:

(A) Substituted hydroxy compounds Alkyl phenols 30-0-4 onito .n

(2) Aliphatic alcohols R' o-(c 'H.0 ,,H (3) Partial esters of polyhydricalcohol and aliphatic acids (glycerol, sorbitol, or sorbitol anhydride):

RCOOCH2 CHO-(O:H4O):H

CHzO-(C:H4O),H

(4) Partial ethers of polyhydric alcohols and aliphatic alcohols:

RCH:O-CH:

H-O-(OzHiOhH HIO(CIH4O)1H (B) Substituted thio-alcohols (mercaptans)R'S-( 2 4 (C) Substituted acids (1) Aliphatic acids R'--COO (C l-I 0 H(2) Alkyl phosphates (3) Tertiary carbon fatty amine (F) Substitutedethylene oxinated alkyl phenols (1) Alkylated polyether sulfates R-O-0oeHt0),-o-s-oNa o (2) Alkylaryl polyether sulfonates nO-ooenton-s-om (G)Condensation of ethylene oxidev with propylene oxide and propyleneglycol 'noweHeo)nceHeonweHeoie (H) Condensarion with itself (solid highmolecular In most of the above compounds, the ethylene oxide componentwill preferably constitute from about 60 to about 90% by weight, theextent of water solubility often being determined by the ethylene oxidecontent. Propylene oxide may be substituted for ethylene oxide in theabove examples and often mixtures of ethylene oxide and propylene oxidecondensation products may be employed. Ethylene oxide is, however,generally much preferred.

Some specific examples of suitable addition agents for use in accordancewith our invention are condensation products of ethylene oxide with:

It will be seen that organic'compounds having an active hydrogen atomattached to an oxygen, sulphur, or nitrogen atom may thus be condensedwith the alkylene oxide (ordinarily ethylene oxide or propylene oxide inorder to obtain the desired water solubility) to produce the additionagents for use in our new baths from which lead is to be deposited onferrous articles by chemical displacement. In most cases this additionagent will constitute only about 1% by weight of the coating bath orsolution. From about 0.1 gram per liter to about grams per liter may beemployed but there is seldom advantage in using over 1 gram per liter.

The following is given as a preferred illustrative example of thecomplete operation. approximately 170 F. and 33 grams per liter oflitharge and 18 milliliters per liter of 90% formic acid are added andstirred until dissolved. Alternatively, 43 grams per liter of leadformate may be added. This will aiford a lead ion concentration ofapproximately 30 grams per.

liter. The pH may then be adjusted by slight additions Water is heatedto h 6 of lithar'ge or formic acid to bring it within the 3.4-4.2 range.One gram per liter of an addition agent formed by condensing one mole ofnonyl phenol with 15-30 mob of ethylene oxide is added to the bath. Thetemperature of the bath is raised to about 200 F. and the ferrousarticle immersed therein for a period of from about 4 to about 1.0minutes, ordinarily about 7 minutes. The metal surface should, ofcourse, be clean for best results' A lead deposit is obtained of fromabout 0.000075 to about 0.000150 inch in thickness. If immersed for arelatively long period at lower temperatures (e. g. F.) a heavierdeposit may be obtained. The higher the temperature and the shorter theimmersion pe riod, the thinner the deposit produced. As additional workis processed, the lead ion concentration is depleted and the amount ofiron in solution increases. The lead ion concentration may convenientlybe checked by measuring the specific gravity of the bath, titrating todetermine the iron concentration, and then reading the lead ionconcentration from a graph based on known concentrations. The pH shouldbe checked periodically and adjusted as necessary. Oxidation of the ironfrom ferrous to ferric form occurs (air may be bubbled through the bathto hasten this) and the iron precipitates as ferric hydroxide. When thelead ion concentration drops to about 15-20 grams per liter, more leadformate may be added again to raise the concentration to 30 grams perliterv Eventually the solution will become saturated with ferrousion'(at about 35 grams per liter of ferrous ion) and thebath should bereplaced. If the bath should be allowed to reach too low a temperature,lead formate may crystallize out but will redissolve on heating.

' Qne of the interesting features of the novel coating solution of thisinvention is its versatility in mode of application, Satisfactorydeposits can be obtained by immersion, brushing on, flow coating, andspraying' The last-named method is often especially advantageous sincemuch of industry is geared to spray coat various types of materials forchemical surface treatment of metals as in phosphating, chromating andthe like. The mode of application will often be dictated by thefacilities already available and the size and shape of the articles tobe coated.

As might be expected, the rate of deposition is greatest at the start ofthe operation and gradually lessens with time. Sound deposits having athickness of 0.0003 inch may be obtained and even more.

it will, of course, be appreciated that before the work is coated itshould first be free of all oil, grease and dirt. Such prior cleaningoperation may, for example, include vapor degreasing or preferablytreatment with a chemical cleaner such as the commercially availablealkali, emulsion or two-phase cleaners. Following such cleaning operation, the work should be thoroughly rinsed in water, and if free ofrust and scale it need not be acid pickled. If pickling should berequired, however, the work will again be thoroughly water rinsed aftercompletion of the pickling operation. It will then be conveyed to theprocessing tank or spray booth Where metallic lead is deposited thereonto the desired predetermined thickness. Subsequently, the work will berinsed first in cold water and then in hot Water to facilitate drying,forced warm air drying being preferred.

The lead coated article may receive supplemental surface treatments suchas chromat-ing, oxalating, sulphating and phosphating in dilutesolutions. Under proper conditions, the lead may be bright flowed whichfurther enhances its corrosion retarding ability. As a rule, hoW- ever,these various supplemental treatments will be found unnecessary. Morefrequently, the finished coated article will merely be painted or oiled,the surface being particu larly suited therefor.

Corrosion and Weathering tests have shown ferrous articles coated inaccordance with the present invention to be exceptionally resistant tocorrosion. Ferrous articles I? v lead. coated in accordance with thisinvention will withstand the conventional salt spray test for a periodof time approximately equal to that achieved by an electroplated zinccoating.

The employment of lead coatings to facilitate deep drawing operationsand the drawing of wire, and particularly the drawing of steel wire, hasbeen suggested since it has been determined that lead is a lubricant insuch drawing operations superior to the usual greases, oils, soaps,emulsions, etc., but such other methods have been generally adopted inthe industry for the reason that no economical method of applying thelead coating has previously been available. Thin lead coatings may alsoserve efiiciently as a bearing metal in other applications.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed. 7

We therefore particularly point out and distinctly claim as ourinvention:

1. The method of forming a substantial sound adherent protective leadcoating on ferrous articles which comprises subjecting such article tothe action of a water solution of lead formate and the at least slightlywater soluble condensation product of ethylene oxide and an organiccompound, the solution having a pH of from 2.5 to 5.0 and a lead ionconcentration of from 1 to 80 grams per liter, for a period of timesufficient to deposit a continuous corrosion-resistant lead coating onsuch article by chemical displacement.

2. The method of forming a substantial sound adherent protective leadcoating on ferrous articles which comprises subjecting such article tothe action of a water solution of lead formate and the at least slightlywater soluble condensation product of ethylene oxide and an organiccompound, the solution having a pH of from 3.4 to 4.2 and a lead ionconcentration of from 10 to grams per liter, the temperature of thesolution being above 170 F., per a period oftime sufficient to deposit acontinuous corrosion-resistant lead coating on such article by chemicaldisplacement.

3. A bath suitable for the coating of ferrous articles with lead by achemical displacement reaction comprising a water solution of leadformate and the at least slightly water soluble condensation product ofethylene oxide with an organic compound having an active hydrogenattached to an O, S, or N atom, said solution having a pl-i of from 2.5to 5.0 and a lead ion concentration of from 1 to grams per liter. 7

4. A bath suitable for the coating of ferrous articles with lead by achemical displacement reaction comprising a water solution of leadformate and the at least slightly water soluble condensation product ofethylene oxide with an organic compound having an active hydrogenattached to an O, S, or N atom, said solution having a pH of from 3.4 to4.2 and a lead ion concentration of from 10 to 40 grams per liter, thetemperature of the bath being at least F.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Nov. 27,

1. THE METHOD OF FORMING A SUBSTANTIAL SOUND ADHERENT PROTECTIVE LEADCOATING ON FERROUS ARTICLES WHICH COMPRISES SUBJECTING SUCH ARTICLE TOTHE ACTION OF A WATER SOLUTION OF LEAD FORMATE AND THE AT LEAST SLIGHTLYWATER SOLUBLE CONDENSATION PRODUCT OF ETHYLENE OXIDE AND AN ORGANICCOMPOUND, THE SOLUTION HAVING A PH OF FROM 2.5 TO 5.0 AND A LEAD IONCONCENTRATION OF FROM 1 TO 80 GRAMS PER LITER, FOR A PERIOD OF TIMESUFFICIENT TO DEPOSIT A CONTINUOUS CORROSION-RESISTANT LEAD COATING ONSUCH ARTICLE BY CHEMICAL DISPLACEMENT.